Preparation of 2, 3-dinitronaphthalene



United States Patent 3 085,115 PREPARATION OF 2, 3-DINITRONAPHTHALENE Melvin Look, El Cerrito, and Howard L. Cheifetz, Berkeley, Calif., assignors to Fundamental Research Company, Berkeley, Calif., a partnership No Drawing. Filed Oct. 27, 1960, Ser. No. 65,280 1 Claim. (Cl. 260-645) This invention relates to a naphthalene derivative and its preparation. More particularly, it is concerned with 2,3-dinitronaphthalene and a commercially practical process for its preparation.

Of all the ten theoretically possible dinitronaphthalenes the 2,3-dinitro has heretofore been regarded as the rarest, and has been prepared only in research quantities and then only by complicated procedures and in poor yields. To the best of our knowledge, no commercially feasible method has been described in the literature for the preparation of this compound, which would appear to have wide potential use as an intermediate, particularly in the polymer, plastics, pharmaceutical and dyestutf industries.

A principal object of the invention therefore is a novel process for the preparation of 2,3-dinitronaphthalene.

A further object of the invention is a process for the preparation of 2,3-dinitronaphthalene substantially free from other isomeric compounds.

Another object of the invention is a cyclic process for the preparation of 2,3-dinitronaphthalene.

Still another object of the invention is a commercially practical process for the production of 2,3-dinitronaphthalene in which this 'hitherto rare product is obtained in relatively good yield and in which the formation of waste products is minimized.

The manner of attainment of these and other objects of the invention will become evident on further reading of this specification and the claim.

The process of our invention, by which for the first time the production of 2,3-dinit-ronaphthalene is made both practical and commercially attractive, comprises in essence (l) the nitration under highly specific conditions of (a) a particular Diels-Alder adduct containing a naphthalene moiety, or (b) the Z-nitro derivative of that adduct, whereby the naphthalene moiety is dinitrated in the 2,3-positions; land (2) pyrolysis of the dinitrated adduct under rigorously prescribed conditions to yield 2,3-dinitronaphthalene.

In US. Patent No. 2,658,926 it is disclosed that two molecules of hexachlorocyclopentadiene may be added unsymmetrically to one molecule of naphthalene in a Die-ls-Alder (diene) synthesis. In US. Patent No. 2,658,913 it is disclosed that the adduct resulting from the diene synthesis just referred to may be nitrated, the nitration being primarily in the beta position. A co-pending application of H. L. Cheifetz, Melvin Look, and J. R. McLaughlin, Serial No. 1,447, now Patent No. 3,065,278, filed January 11, 1960, states that there is a minor amount of alpha-unrated adduct in the mononitrated adduct, and that this alpha-nitrated product may be dinitrated to the 1,3-dinitro adduct by further treatment with nitrating acid for a relatively short period of time, the beta-nitrated adduct is essentially unaffected by this treatment and accordingly, if so desired, may be separated from the 1,3- dinitro adduct by selective solvent extraction or selective reactivity, although on a practical production scale it is preferred to efiect the separation on the post-pyrolysis products, as described in Example 4 below.

We have now found that it is possible to force the dinitration of the beta-nitro-a'dduct also, forming primarily the 2,3-dinitro-adduct, by treatment for a prolonged period, as, for example, for '12 to 24 hours, with fuming nitric acid, admixed with oleum, at about the reflux tem- 3,085,115 Patented Apr. 9, 1963 perature of the fuming nitric acid. By this method we have carried the dinitration to the point where approximately one-half to two-thirds of the mono-nitro-adduct has been dinitrated. Further dinitration does not appear economical, since the drastic nitrating conditions employed tend to oxidize a portion of the dinitrated prodnot to an acid-soluble by-product; and this material is further objectionable in that it does not lend itself to pyrolytic cracking, but instead forms coke in the cracking chamber. The 2,3-dinitro-addnct has the empirical formula C H Cl (NO and the structure While the process of our invention results from our discovery that dinitration of the 2-nitro-adduct may be forced .by the drastic and prolonged nitration described above, it is not necessary to start with the mono-nitrated adduct for the dinitration treatment. In many cases, as a practical operating procedure, it will be found simpler to carry out the dinitration in a. single step on the unnitrated adduct of hexachlorocyclopentadiene and naphthalene, designated hereinafter as DHA, either in solid form or in solution, and to separate the 2,3-dinitro-naphthalene from other reaction products in a later stage of the process. Or, if desired, the 2,3-dinitrated adduct may be concentrated and separated from the 1,3-dinitrated adduct and mono-nitrated adduct by solvent extraction. We have found that methanol serves as an excellent ex tractant for the 2,3-dinitrated adduct, with much lower solubility for the mono-nitro compound, and practically no solubility at all for the 1,3-dinitro compound. The concentration of the 2,3-dinitrated adduct provided by solvent extraction may be used to advantage not only in the subsequent steps of the process of our invention, but is of particular value when the dinitrated adduct is to be utilized in other chemical reactions.

As previously noted, the second essential step of our process for producing 2,3-dinitronaphthalene is the pyrolysis of the 2,3-dinitro adduct. The desired products of the pyrolysis are 2,3-dinitronaphthalene and hexachlorocyclopentadiene, the latter, of course, being one of the generators of the original adduct.

We have found that the 2,3-dinitro-adduct may be pyrolyzed directly by batch cracking only at the expense of a very considerable loss of its generators. We have also found, however, that if the nitrated adduct or adduct mixture is made into a slurry with any suitable carrier liquid and pyrolyzed by continuous film cracking at temperatures of about 375 to about 450 C., the cracking is rapid and complete, and yields of 2,3-dinitronaphthalene of 65 percent or more of the amount theoretically available are regularly obtained. In film cracking it is advisable to have the distance between the cracking and condensing surfaces as small as conveniently possible, on the order, for example, of one-half inch to two inches. The conventional wiped-film molecular still is well suited for this cracking. Reduced pressures are not essential for the success of this cracking operation, although the use of sub-atmospheric pressures during pyrolysis tends to improve yields and reduce coke formation.

As noted above, the liquid used in forming the slurry to be pyrolyzed may be any suitable carrier, inert and thermally stable at the cracking temperatures employed, as, for example, the liquid chlorinated naphthalenes and diphenyls. We have found a particular advantageous carrier liquid, however, to be hexachlorocyclopentadiene itself. This liquid has density and solubility characteristics such that the suspended adduct particles settle out only very slowly. Moreover, and obviously very important, hexachlorocyclopentadiene is one of the products of pyrolysis, so that subsequent separation of a foreign carrier is thereby avoided, and it can be readily removed from the cracking zone by operating under a vacuum. The recovery of the hexachlorocyclopentadiene carrier liquid and re-formed generator, and their random re-utilization in the process, add to the commercial attractiveness of the process. Still another and unobvious advantage of using hexachlorocyclopentadiene as the carrier liquid is its low solubility for 2,3-dinitronaphthalene, so that much of the latter separates promptly from the liquid on the cold wall of the cracker and may be recovered in pure form by simple filtration. A more slowly separating and less solid product may be further purified by crystallization first from concentrated (96 percent) sulfuric acid, in which 2,3-dinitronaphthalene is quite soluble at 75 C. but only slightly soluble at room temperature, followed by crystallization of the acid-soluble fraction from a lower alcohol, such as isopropanol, which has less solubility for the concomitant 1,3-dinitronaphthalene than for the 2,3-isomer. This alternating type of crystallization may be continued to achieve a complete separation of the isomers. The mother liquor from the original crystallization may be vacuum distilled to recover separately hexachlorocyclopentadiene and Z-nitronaphthalone.

Typical procedures for the preparation and recovery of 2,3-dinitronaphthalene according to the process of our invention are set forth in the following examples, which are given only for the purposes of illustration, not of limitation. Example 1 sets forth the procedure for synthesizing the 2,3-dinitro dihexachlorocyclopentadiene adduct of naphthalene, hereinafter for convenience designated as 2,3-Di-NDHA, by prolonged drastic nitration of the un-nitrated adduct, DHA, of US Patent No. 2,658,- 926 previously referred to. Examples 2 and 3 describe the preparation of the 2,3-dinitro adduct starting with the mononitrated adduct. Example 4 describes the pyrolytic cracking of the 2,3-Di-NDHA to produce 2,3-dinitronaphthalene, with the simultaneous regeneration of the hexachlorocyclopentadiene generator.

EXAMPLE 1 Synthesis of 2,3-Di-NDHA From DHA To a stirred mixture of 1940 grams anhydrous nitric acid, 1300 grams sulfuric acid (100 percent), and 150 grams sulfur trioxide (the last two in the form of oleum) was added over a period of an hour 500 grams (0.74 mole) DHA. The mixture was heated at the reflux temperature of the nitric acid, ranging between 87 and 91 C., for 12 hours. The slurry was allowed to cool to room temperature and was then filtered. The filter cake was triturated with ice water, then refiltered, washed with water, and dried. The product consisted of 40 percent 2,3-Di-NDHA, 15 percent 1,3-Di-NDHA, and the remainder 2-NDHA and oxidation products.

EXAMPLE 2 Synthesis of 2,3-Di-NDHA From DHA and NDHA in Solution In this example the mononitrated diadduct, NDHA, was both prepared, and subsequently employed for di nitration, in methylene chloride solution in accordance with the teachings of the c-opending application of Julius Hyman and Herbert P. C. Lee, Serial No. 1,427, filed January 11, 1960, now Patent No. 3,065,277. A solution of 6 Normal nitric acid in methylene chloride was prepared by mixing 378 ml. of percent nitric acid with 1122 ml. of methylene chloride. This solution was cooled in a Water bath held at 30 C. while 500 grams of DHA was added. The mixture was then stirred for 30 minutes, at the end of which time the DHA was both dissolved and completely mononitrated. In a reaction vessel arranged for distillation of solvent, the methylene chloride solution was added in a small stream over a period of two hours to a stirred mixture of 1940 grams of 100 percent white fuming nitric acid, 1300 grams of 100 percent sulfuric acid, and grams of sulfur trioxide (the last two in the form of oleum) that was heated to and maintained at 60 to 70 C. The solvent along with nitric acid flashed off during the addition, and the reaction mixture was then heated to between 87 and 91 C. to remove the last trace of the methylene chloride and to precipitate the mono-nitrated DHA into the oleumnitric acid mixture in a very desirable, finely divided form. The acid-solvent distillate had substantially the same composition as the 6 Normal acid-methylene chloride solution used in the first step of the process, and so was saved and subsequently used for treatment of a further portion of DHA. The setup of the flask containing the slurry of mono-nitrated adducts (referred to herein as NDHA) in the oleum-nitric acid mixture was then rearranged for reflux instead of for distillation, and the dinitration mixture refluxed at a temperature maintained between 87- 9l C. for an additional 18 hours. The product of nitration was isolated as in Example I. Infra-red spectroscopic examination indicated that the product contained approximately 50% of 2,3-Di-NDHA, 15% of 1,3- Di NDHA and the remainder NDHA and oxidation products.

EXAMPLE 3 Synthesis of 2,3-Di-NDHA From Solid NDHA In this example the mononitrated adduct, NDHA, was employed in solid form. The procedure followed was exactly that set forth in Example 1, except that the solid mononitrated adduct, NDHA, was substituted for the un-nitrated adduct, DHA, and the reaction mixture was heated for 24 hours.

EXAMPLE 4 Pyrolysis of Di-NDHA Five hundred grams of the powdered Di-NDHA reaction products obtained from Example 2 was intimately mixed with 600 ml. hexachlorocyclopentadiene and the slurry pyrolyzed by pulsed pump addition to a wipedfilrn molecular-type still, 2 inches in diameter and 8 inches high, operated at atmospheric pressure and held between 375 and 450 C. external temperature. The average time for pyrolyzing a batch of this volume was two hours, or nearly 4 grams Di-NDHA per minute. About half of the 2,3-dinitronaphthalene produced precipitated in pure form on the cold finger of the still, and was removed at the end of the run. The remaining mixed 1,3- and 2,3-dinitronaphthalene gradually crystallized essentially completely from the distillate, leaving only Z-nitronaphthalene remaining in the hexachlorocyclopentadiene. The hexachlorocyclopentadiene and 2- nitronaphthalene were separated from each other by vacuum distillation. Separation of the mixed 1,3- and 2,3-di-nitronaphthalene was effected by dissolving the residue in 96 percent sulfuric acid heated to 75 C. for two hours. On cooling, pure 2,3-dinitronaphthalene separated out and Was recovered by filtration. The acid filtrate was quenched with ice, and the mixture of 1,3- and 2,3-dinitronaphthalene which precipitated was crystallized from isopropanol to produce pure 1,3-dinitronaphthalene, leaving a minor amount of 1,3- and 2,3- dinitronaphthalene eutectic mixture. This mixture was added to other similar residues, and again crystallized from 96 percent sulfuric acid, yielding another crop of pure 2,3-dinitronaphthalene. The overall yield of 2,3- dinitronaphthalene was estimated at 49 grams, or approximately two-thirds of the theoretical, based on the infra-red spectrophotometric analysis of the starting dinitrated adduct mixture.

It is obvious that the procedures described in the foregoing exposition and examples lend themselves to numerous modifications which will suggest themselves to those skilled in the chemical and chemical engineering arts involved. All such modifications and ramifications are deemed to be comprehended within the scope of the invention, aS limited only by the claim.

We claim:

The 2,3-dinitro-Diels-Alder adduct of two moles of hexachlorocyclopentadiene and one mole of naphthalene, said adduct having the empirical formula 20 e 12( -2)2 and having the property of cracking at temperaturepressure conditions on the order of 375-450 C. and atmospheric pressure to produce hexachlorocyclopentadiene and 2,3-dinitronaphthalene.

References Cited in the file of this patent UNITED STATES PATENTS 2,658,913 Hyman et a1 Nov. 10, 1953 

